Serum leptin levels in Mexican Americans and non-Hispanic whites: Association with body mass index and cigarette smoking

Leptin is the protein product of the obesity (OB) gene in humans. To date, no study has correlated serum leptin levels with ethnicity, cigarette smoking, or other cardiovascular risk factors. In this study, serum leptin levels were measured in 100 Mexican Americans and 50 non-Hispanic whites who participated in the San Antonio Heart Study. Mexican Americans had higher levels of serum leptin than age- and sex-matched non-Hispanic whites (21 vs. 16 ng/mL). However, the leptin levels were similar in the two groups after controlling for body mass index (BMI). Women had higher levels of serum leptin than did men (24 vs. 9 ng/mL; P < 0001). There, was a strong association between leptin levels and BMI (r = 0.91 in non-Hispanic white men; r = 0.77 in non-Hispanic women; r = 0.81 in Mexican American men; and r = 0.78 in Mexican American women). A model containing age, sex, and BMI explained 79% of the variance in serum leptin levels. After adjustment for age, sex, and BMI, current cigarette smokers had significantly lower leptin levels than never-smokers (p < 0.05). The results suggested that human obesity was associated with leptin-resistance rather than leptin-deficiency. Leptin levels were positively associated with BMI in this cross-sectional analysis. Cigarette smoking may increase sensitivity to leptin, since cigarette smokers had lower leptin levels than did nonsmokers with the same BMI.